Greenland Ice Sheet Ice Slab Expansion and Thickening

Abstract

Firn is found above the equilibrium line and consists of interannual snowpack, the density of which increases by compaction through burial but also due to percolation and refreezing of surface meltwater (Braithwaite et al., 1994;Brown et al., 2011;Pfeffer & Humphrey, 1998). Firn has the potential to trap and store meltwater within its pore space, thereby buffering the GrIS contribution to sea level rise (Harper et al., 2012;Pfeffer et al., 1991).In the percolation zone, where surface melt rates are substantial but usually do not deplete the seasonal snow completely, the fate of meltwater varies mainly with annual snowfall. Where snowfall rates are high (∼1,000 ± 400 mm w.e. per year), mostly in southeast and south Greenland, liquid water percolates to a depth where it forms perennial firn aquifers (Forster et al., 2014;Miège et al., 2016;Miller et al., 2022). Conversely, in regions where accumulation rates are lower and which have recently experienced significant melting, ice slabs several meters thick can form-mostly along the west, north and northeast of the GrIS (MacFerrin et al., 2019;Miller et al., 2022). In these regions, increased meltwater percolation during several successive summers fused centimeters-scale ice lenses into increasingly contiguous ice layers tens of centimeters thick and eventually

Climatic Drivers of Ice Slabs and Firn Aquifers in Greenland

“…In contrast, the modeled total aquifer extent increased gradually since the early 2000s and decreased after 2012. Figure S7 and Table S1 in Supporting Information S1 show that recent changes in ice slabs in SW and aquifers in SE agree broadly with observed changes (Horlings et al, 2022;Jullien et al, 2023).…”

“…At higher melt rates, aquifers eventually disappear as the system transitions toward the ice-slab-only regime. Our (Brangers et al, 2020;Jullien et al, 2023;MacFerrin et al, 2019;Miège et al, 2016;Miller et al, 2020Miller et al, , 2022Shang et al, 2022).…”

“…Recalculating the modeled slab content while excluding the areas not sampled by OIB significantly improves the agreement, often falling within one standard deviation (blue lines in Figure 2). Secondly, ice is treated as permeable in IMAU-FDM whereas Jullien et al (2023) observed that ice slabs grow mostly by accretion on top. Therefore, at low melt rates, the formation of multiple thinner ice lenses is more likely in the model.…”

“…Given typical burial rates and ice velocities, the majority of ice slabs remain in the same model grid cell they were created in. Again following MacFerrin et al (2019) and Jullien et al (2023), we only consider ice in the top 20 m of firn. Grid cells with a mean negative SMB during 1960-1980 are considered ablation zone, without firn, and are excluded from the analysis.…”

“…Ice slabs, ice layers of at least 1 m thick, have been detected inside the firn of the western and northern GrIS (Jullien et al, 2023;MacFerrin et al, 2019;Machguth et al, 2016). They limit meltwater storage and facilitate runoff (MacFerrin et al, 2019).…”